The present invention applies to improvements in scrap preheating systems of the type shown in U.S. Pat. No. 3,985,497 issued Oct. 12, 1976 and application Ser. No. 710,750 filed Aug. 2, 1976, now U.S. Pat. No. 4,083,675, and more specifically to improvements in the roof structures of such preheater hoods.
Scrap preheaters are finding increasing use in the basic iron and steel industry as an effective means for recovering and reusing scrap iron and steel. Scrap preheaters accomplish at least two basic functions. The first is to burn off and remove from the scrap such undesirable elements as water, grease and the like. Additionally, it is preferable to charge preheated scrap into furnaces, such as induction furnaces, in order to reduce the overall time for the batch to reach pouring temperature.
Scrap preheaters are basically elongate tunnel like devices through which a conveyor passes which carries the scrap steel. Gas or oil burners are positioned within the tunnel and the flames from the burners are directed upon the scrap material to heat the material and remove the moisture and hydrocarbons from the material. Thereafter, the preheated and cleansed material is charged into a melting furnace.
A more detailed description of a preferred structure of scrap preheating assembly and the operation thereof is set forth in the aforementioned patent and patent application. The disclosure in the aforementioned patent and patent application is hereby incorporated herein by reference thereto and reference should be made to the patent and patent application for a more detailed understanding of the details of the entire structure of a preheater hood as well as the operation thereof.
A typical preheater hood, for example of the size generally shown in the aforementioned patent and patent application, would be approximately 25 feet in length and 4 feet wide with a spacing of approximately 2 feet between the upper surface of the conveyor and the under surface of the roof of the preheater hood. The roof assemblies of preheaters heretofore known and of the type set forth in the foregoing patent and patent application are precast in one or two large sections and the entire roof assembly is then supported upon the side walls. The roof assemblies alone of preheaters heretofore known, of course depending upon the size, range in weight from 5 to 20 tons.
The side walls of the roof assemblies of such preheater hoods are formed of metal casings and are lined with a refractory material usually several inches thick. The refractory material is subjected to extreme temperatures and temperature changes as well as excessive vibration resulting primarily from the conveyor which is usually of a vibratory type. Over a period of time, the refractory material, more particularly that in the roof of the preheater hood, becomes loose and otherwise will generally suffer from the effects of the heat extremes and vibration. Additionally, the conveyor itself is subjected to extreme temperature due to the flames striking the scrap upon the conveyor and the conveyor itself very often is in need of repair.
When maintenance is required upon the conveyor and/or the preheater hood of the designs heretofore known, extreme difficulty is encountered. Firstly, the spacing between the conveyor and the roof assembly makes it very difficult to work upon either the conveyor or the under surface of the preheater roof as well as the side walls thereof. Additionally, the large cranes and other equipment which is usually present during the installation of the equipment is no longer there and extreme difficulty is encountered in raising the extremely heavy roof structures of the preheaters in order to expose the roof and side walls of the preheater as well as the conveyor associated therewith.